Sensitive-Layer Fabrication

Fluorescence resonance energy transfer (FRET) has also been used very often to design optical sensors. In this case, the sensitive layer contains the fluorophore and an analyte-sensitive dye, the absorption band of which overlaps significantly with the emission of the former. Reversible interaction of the absorber with the analyte species (e.g. the sample acidity, chloride, cations, anions,...) leads to a variation of the absorption band so that the efficiency of energy transfer from the fluorophore changes36 In this way, both emission intensity- and lifetime-based sensors may be fabricated. 

In recent years, there are more applications based on the layer-by-layer fabrication techniques for CNT-modified electrodes. This technique clearly provides thinner and more isolated CNTs compared with other methods such as CNT-composite and CNT coated electrodes in which CNTs are in the form of big bundles. This method should help biomolecules such as enzymes and DNA to interact more effectively with CNTs than other methods, and sensors based on this technique are expected to be more sensitive. Important biosensors such as glucose sensors have been developed using this technique, and further development of other sensors based on the layer-by-layer technique is expected. 

Keith, J. Hess, L. C. Spendel, W. U. Cox, J. A. Pacey, G. E., The investigation of the behavior of a long period grating sensor with a copper sensitive coating fabricated by layer by layer electrostatic adsorption, Talanta 2006, 70, 818 822... 

As the chip layout is not particularly optimized for a TO-package, a DIL package was used. In contrast to the previous sensor fabrication process, the sensitive layer was deposited after packaging, and an on-chip annealing was performed. 

In order to establish good electrical contact to the sensitive layer, it was necessary to coat the electrodes with a metal stack of Ti/W (diffusion barrier and adhesion layer) and Pt. The usage of a shadow mask during the metal deposition ensures full compatibility with other MEMS processing steps so that it is possible to fabricate various CMOS-MEMS devices on the same wafer. 

Schlautmann, S., Besselink, G.A.J., Radhakrishna Prabhu, G., Schasfoort, R.B.M., Fabrication of a microfluidic chip by UV bonding at room temperature for integration of temperature-sensitive layers. J. Micromech. Microeng. 2003, 13, S81-S84. 

The effects of the generation-layer fabrication variables on the sensitometry of a dual-layer photoreceptor prepared with bis(4-dimethylaminophenyl) squaraine (X = H in Appendix 2) have been extensively investigated by Law (1987). The charge acceptance, dark discharge, sensitivity, and the residual... 

It is clear that the material and geometry of the electrodes can influence gas sensor behavior. Many researchers are investigating the fabrication of gas sensors using nanoparticulate materials as the sensitive layer. While it is possible to use normal sized electrodes with widths and separations of several microns for these devices, it is of interest to examine the changes in response which are obtained when nanoelectrodes are used i.e. contacts of comparable dimensions to a single particle - around 5 nm. Potential advantages of nanoelectrodes include ... 

It is more difficult to fabricate semitransparent than opaque devices because the thickness of the sensitive layer is an added critical parameter not important in the opaque structure. (Improper thickness in the semitransparent device would limit both the range of useful spectral response and overall quantum efficiency [5.29].) Most new photoemissive surfaces, particularly NBA, are now investigated initially in their opaque ( reflection mode , RM , or front illuminated ) form, which usually offers the highest initial optical and electron-emissive quantum efficiency, and only after determining optimum thickness and optimum fabrication methods are new surfaces produced in the semitransparent ( transparent , transmission mode , TM , or back illuminated ) form. Eventually both forms are offered commercially in several variants, each optimized for selected parameters such as low cost, peak response at a specific... 

Ba " ", Cs, NH4", Ag" ") and anions (NOi j Cl , HCOi ). Solid-state ISEs (coated wire electrodes) have also been developed in which the sensitive membrane is coated directly onto a metal wire, usually a silver-silver halide. While these have the advantage of being small and easy to fabricate, they have been noted for their unpredictable properties and suffer from lifetime and stability problems. More sophisticated approaches involve the use of semiconductor planar fabrication technologies to deposit ion-sensitive layers onto semiconductor substrates to produce ion-selective field-effect transistors. These are conceptually very attractive but it has proven very difficult to produce devices as good as the equivalent ISE. 

Barsan and Weimar (2001) considered thick-flhn technology an excellent technique for fabricating many types of gas sensors because it allows one to make the highly porous sensitive layers of nano-structured films. In general, thick-flhn technology has several significant advantages for sensor development ... 

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